Heat-sealable packaging films have a long history of use with high speed packaging equipment such as vertical-form-fill-and-seal, side-seal, and flow-wrap machines. The film is used to wrap and seal a large variety of items including soft and hard goods as well as cooked and uncooked foods. Heat-sealable films fall into two main film categories: polymer materials with a wide melt temperature range which are practical to melt-seal to itself and polymer materials with a narrow melt temperature range which are not practical to melt-seal together. The packaging film referred to herein is in the narrow melt temperature range, used for its overall high melt temperature and good barrier qualities.
Known packaging films are typically made of a pliable high melt temperature substrate which is laminated to a low melt temperature film so the resultant film is heat-sealable to itself. This packaging category is known as Flexible packaging. For the final package to be strong, the film must heat-seal together in a predictable manor without melting onto the hot sealing device.
To accomplish this a high temperature film is used as a substrate to which a suitable low temperature film is laminated forming a unified material. The high and low temperature films must be of a compatible nature so they can be adhered to each other using a suitable laminating adhesive. The high temperature layer forms the package's outside structure while the low temperature layer will act as the package's inside heat-sealing component. During the packaging process the laminated film is wrapped around a contained item then hot sealing irons or jaws are applied to appropriate areas melting the low temperature film components together to form the package's seals.
To produce an effective heat-sealed package the film must be wrapped so the inside laminated low temperature layer is facing itself, inside layer to inside layer. The hot sealing irons are applied to the film's outside high temperature substrate which conducts the heat through to the two adjacent low temperature layers, melting them together to effectively form a seal between the two high temperature film substrates. With low temperature film facing low temperature film the applied heat will melt the low temperature film layer without melting the high temperature substrate. In this way the low temperature layer acts like hot-melt glue to stick the two high temperature layers together.
Since known packaging films are made using the above described laminations, film surfaces can easily be sealed together at any location where the two inner surfaces come into contact with one another in the presence of a high temperature component. Typical heat-seal temperatures are in the 250 degree F. range.
Barrier submersion cooking is a cooking process wherein a cooking pouch contains a food item, the pouch being effectively dimensioned so that when the pouch is placed into a hot liquid cooking medium a vent remains above a top surface of the liquid cooking medium. Typically a rack holding the food containing pouch is lowered into the liquid cooking medium to an effective depth wherein the food item is below the top surface of the liquid cooking medium and the vent is above the top surface of the liquid cooking medium.
The barrier submersion cooking pouch is formed of a pliable material, for example, a polymer film with a melting point above the temperatures conventionally used in hot oil frying processes. The pouch pliability causes the pouch to collapse on itself when exposed to hydrostatic pressures within the cooking medium and the pouch material has a heat transfer rate that allows the food to fry without being directly exposed to the cooking medium. Typically, barrier submersion cooking is conducted at about 350 degrees F. Barrier submersion cooking results in better moisture retention, more efficient flavor infusion, and reduced cooking time.
At the temperature used in the barrier submersion cooking process the water contained in the food will rapidly come to a boil requiring an adequate path for venting of the resulting steam pressure. For this reason a steam vent is formed in the pouch at a location far enough from the food to keep juices from spilling out of the pouch and at a location that does not allow the cooking medium to enter the pouch.
During the barrier submersion cooking process it is easy for the cooking pouch's inside surfaces to come together and potentially seal off the steam vent path. With conventional pouch designs the hydrostatic pressure of the hot cooking medium will press the pouch together causing the facing low temperature layers to stick together and seal off the steam escape path. The resulting steam pressure will rupture the cooking pouch, ruining the contained food.
Conventional steam pouches are designed to vent steam when used in microwave cooking. In microwave cooking the vent needs to be sealed closed for shipping purposes and only open when cooked food produces sufficient steam pressure to cause the vent to open and release sufficient steam pressure so the pouch will not rupture. In this type of steam pouch cooking steam is only reduced to a safe level because a steam bubble is preferred to maintain an umbrella of hot steam over the food until it is fully cooked and the heat source is removed.
With barrier submersion cooking a free flow release of steam pressure must be allowed so the steam does not build a bubble which would cause a steam pressure gap to form between the film and the surface of the food. This steam pressure gap would greatly reduce the temperature seen by the surface of the food. This would result in the food being boiled instead of fried in the areas of the steam bubble.
Accordingly, there is still a continuing need for improved cooking pouch designs. The present invention fulfills this need and further provides related advantages.